Wifi problems in Cyanogen 12.1

To begin with, I'm a noob at these things. Somehow i managed to root my samsung galaxy grand and somehow I threw out Touchwiz(because lag) and somehow I installed the Cyanogen 12.1 for my phone. Now this thing has got a lot of bugs. Although some bugs don't actually bug me, there's this 'wifi shuts down on screen lock' bug that I would want to fix asap. I mean the wifi doesn't actually shut down but it's the connection that goes down. So if I'm downloading something, i need to keep the screen on. If there's no solution to this, please tell me how do i get touchwiz back? I'd prefer a little lag over a weak wifi connection. If possible please provide a Youtube link since I am still not familiar with a lot of terms .Thank You